The present invention relates generally to a method and apparatus for dispensing material onto a substrate, and more specifically, to variable volume positive displacement systems and methods.
There are several types of prior art dispensing systems used for dispensing metered amounts of liquid or paste for a variety of applications. One such application is in the assembly of printed circuit boards and integrated circuit chips. In this application, dispensing systems are used in the process of encapsulating integrated circuits with an encapsulating material and in the process of underfilling flip integrated circuit chips with an encapsulent. Prior art dispensing systems are also used for dispensing dots or balls of liquid epoxy or solder onto circuit boards and integrated circuits. The liquid epoxy and solder is used to connect components to a circuit board or to an integrated circuit. The dispensing systems described above include those manufactured and distributed by Speedline Technologies, Inc, the assignee of the present invention.
A It is desirable to use positive displacement pumps in dispensing systems to effectively control the volume of material dispensed. U.S. Pat. Nos. 4,907,950 and 5,004,404 to Pierrat, which are incorporated herein by reference, disclose positive displacement pumps used to dispense variable quantities of material. The pumps disclosed by Pierrat include a crank-shaft drive that drives a number of pistons and cylinders to couple pressurized material at an inlet of the pump to an outlet of the pump to dispense the material. The pumps disclosed by Pierrat have up to four cylinders, each of which has an inlet port and an outlet port that are respectively coupled on a time-shared basis to the inlet and the outlet of the pump to provide dispensing.
Several problems may be encountered with the type of pump disclosed by Pierrat and other pumps of the prior art. First, the use of numerous pistons and inlet ports can result in a complex design that may have less reliability than desired. Second, such a complex design may result in a pump that is difficult to clean. In many dispensing applications, it is necessary, or at least desirable, to periodically dismantle the dispensing pump to clean material that may become trapped in the pump. Further, the complexity of prior art pumps often times causes them to be more expensive to manufacture than desired, resulting in them being prohibitively expensive for some dispensing applications.
Based on the above, it is desirable to provide a variable volume positive displacement pump that is simpler in design, more reliable and less expensive than dispensing pumps of the prior art.
A first aspect of the present invention is directed to a dispensing system for dispensing a metered quantity of material onto a substrate. The dispensing system includes a base upon which the substrate is placed for receiving dispensed material, a dispensing pump that dispenses material onto the substrate, a container to contain the material prior to dispensing, and a computer control system, coupled to the dispensing pump to control operation of the dispensing pump. The dispensing pump includes an inlet coupled to the container to receive material from the container, an outlet from which material is dispensed, a plurality of dispensing chambers each chamber having a piston movable within the chamber, a valve, positionable to selectively couple the dispensing chambers to the inlet and the outlet, a drive cam, coupled to the pistons, to control movement of the pistons within the chambers to draw dispensing material into the chambers and to dispense dispensing material from the chambers, and a motor coupled to the computer control system and to the drive cam to provide movement of the drive cam to cause dispensing material to dispense from the dispensing pump.
The drive cam may be constructed and arranged to move each of the pistons to an extended position and to maintain each of the pistons at the extended position for a first predetermined dwell time. The drive cam may also be constructed and arranged to move each of the pistons to a retracted position and to maintain each of the pistons at the retracted position for a second predetermined dwell time. The valve may be coupled to the drive cam, such that the drive cam controls operation of the valve. For each of the dispensing chambers, the valve may be positionable between a first position, a second position, and a third position. When the valve is in the first position, the dispensing chamber is operatively coupled to the inlet to receive material from the container, when the valve is in the second position, the dispensing chamber is operatively coupled to the outlet to dispense material, and when the valve is in the third position, the valve blocks the flow of material between the inlet and the dispensing chamber and between the outlet and the dispensing chamber. The drive cam may be constructed and arranged to control the valve such that for each dispensing chamber, the valve moves between the first position and the third position and between the second position and the third position during one of the first predetermined dwell time and the second predetermined dwell time for the piston in the dispensing chamber. The motor may be coupled to the drive cam to provide rotational movement of the drive cam to dispense material, and the drive cam may be coupled to the valve to provide rotational movement of the valve. The dispensing pump may include a detector coupled to the computer control system that detects a home position of the drive cam and provides a signal to the computer control system. The computer control system may include a motor controller for controlling operation of the motor, and a calibration system for obtaining calibration factors for the dispensing pump and providing the calibration factors to the motor controller.
A second aspect of the present invention is directed to a dispensing pump for dispensing a metered quantity of material onto a substrate. The dispensing pump includes an inlet for receiving dispensing material, an outlet from which the dispensing material is dispensed, a plurality of dispensing chambers each having at least one opening to receive material and having at least one opening to dispense material, a circular valve having a first channel and a second channel, a motor, operatively coupled to the circular valve to provide rotation of the circular valve to at least a first rotational position and a second rotational position, such that in the first rotational position of the circular valve, the first channel of the circular valve is operatively coupled between the inlet and one of the dispensing chambers to provide material to the one of the dispensing chambers, and in the second rotational position of the circular valve, the second channel of the circular valve is operatively coupled between the outlet and the one of the dispensing chambers.
The dispensing pump may include a drive cam operatively coupled between the motor and the circular valve. The dispensing pump may include a plurality of pistons, each of the plurality of pistons being disposed in a corresponding one of the plurality of dispensing chambers, and each of the plurality of pistons being coupled to the drive cam.
A third aspect of the present invention is directed to a method of dispensing material onto a substrate using a dispensing system having a dispensing pump, the dispensing pump having a plurality of dispensing chambers each having a piston movable within the dispensing chamber to draw the dispensing material into the dispensing chamber and to dispense the material from the dispensing chamber. The method includes steps of loading the substrate into the dispensing system, positioning the dispensing pump over the substrate, moving one of the pistons in one of the dispensing chambers in a first direction to a retracted position to draw material into the one of the dispensing chambers, maintaining the piston at the retracted position for a first predetermined dwell time, and moving the one of the pistons in a second direction, opposite the first direction, to dispense the material from the one of the dispensing chambers.
The dispensing pump may include an inlet to receive material, an outlet from which material is dispensed, and a valve controllable between a first open position and a first closed position, such that in the first open position, the valve operatively couples the inlet to the one of the dispensing chambers to enable material to flow from the inlet to the one of the dispensing chambers, and in the first closed position the valve prevents material flow from the inlet to the one of the dispensing chambers, and wherein the method further includes a step of moving the valve from the first open position to the first closed position during the first predetermined dwell time.
The method of the third aspect of the present invention may further include steps of moving the piston in the one of the dispensing chambers in the second direction to an extended position to dispense material, maintaining the one of the pistons at the extended position for a second predetermined dwell time, and moving the piston in the first direction to draw material into the one of the dispensing chambers. The valve may be controllable between a second open position and a second closed position such that in the second open position, the valve operatively couples the one of the dispensing chambers to the outlet to enable material to flow from the one of the dispensing chambers to the outlet, and in the second closed position the valve prevents material flow from the one of the dispensing chambers to the outlet, and the method may further include a step of moving the valve from the second open position to the second closed position during the second predetermined dwell time. The method may also include steps of moving the valve from the first closed position to the first open position during the second predetermined dwell time, and moving the valve from the second closed position to the second open position during the first predetermined dwell time.
A fourth aspect of the present invention is directed to a dispensing pump for dispensing material onto a substrate. The dispensing pump includes an inlet to receive dispensing material, an outlet from which dispensing material is dispensed, a chamber housing having a plurality of dispensing chambers each having a piston movable within the dispensing chamber to draw the dispensing material into the dispensing chamber and to dispense the dispensing material from the dispensing chamber, means for moving one of the pistons in one of the dispensing chambers in a first direction to a retracted position to draw material into the one of the dispensing chambers, means for maintaining the one of the pistons at the retracted position for a first predetermined dwell time, and means for moving the one of the pistons in a second direction, opposite the first direction, to dispense the material from the one of the dispensing chambers.
The dispensing pump may further include a valve controllable between a first open position and a first closed position such that in the first open position, the valve operatively couples the inlet to the dispensing chamber to enable material to flow from the inlet to the dispensing chamber, and in the first closed position the valve prevents material flow from the inlet to the dispensing chamber, and means for moving the valve from the first open position to the first closed position during the first predetermined dwell time.
The dispensing pump of the fourth aspect of the present invention may also include means for moving the one of the pistons in the one of the dispensing chambers in the second direction to an extended position to dispense material, and means for maintaining the one of the pistons at the extended position for a second predetermined dwell time. The valve may be controllable between a second open position and a second closed position such that in the second open position, the valve operatively couples the one of the dispensing chambers to the outlet to enable material to flow from the one of the dispensing chambers to the outlet, and in the second closed position the valve prevents material flow from the one of the dispensing chambers to the outlet, and the dispensing pump may further include means for moving the valve from the second open position to the second closed position during the second predetermined dwell time.